The scandals surrounding disgraced leader Bo Xilai and other corrupt cadres are a profound lesson for the Communist party, a spokesman said as delegates gathered in Beijing for China's leadership transition.

Xi Jinping was long ago anointed heir-apparent to Hu Jintao, the country's top leader. But the full makeup of the top political body, the politburo standing committee, will not be known for certain until the members walk out on the dais of the Great Hall of the People in a week's time.

Bo was once tipped as a prospective candidate, but his political fortunes had started to ebb even before the scandal surrounding the death of a British businessman erupted in spring. Bo's wife, Gu Kailai, was convicted earlier this year of murdering Neil Heywood. Bo faces prosecution on unspecified charges, having been accused of corruption and helping to cover up the murder.

"Problems involving Bo Xilai and Liu Zhijun [the former railways minister also facing charges] are severe corruption cases that took place among senior leading cadres. The lessons have been extremely profound," Cai Mingzhao, spokesman for the congress, told a news conference.

He added: "China is in the middle of a social transition and some areas are prey to corruption. The punishment and prevention of corruption is an arduous and ongoing task."

Authorities have repeatedly vowed to crack down on abuses by officials, but many say the problems have intensified over the last decade.

The new leaders face mounting calls for wide-ranging reform from academics, business people and others complaining of policy stagnation under the current administration. But many are pessimistic about the prospects for significant changes in the near future, and the closest Cai came to concrete suggestions was a nod to developing "inner-party democracy".

The 2,268 delegates - slightly fewer than previously thought, as two died after being chosen – will select the new central committee, although there are only a handful more candidates than seats. The latter body then formally appoints the new politburo standing committee. In reality, the new leaders are chosen behind the scenes by the incumbents, party elders and others with influence.